Diffusion of Lithium Salt in Block Copolymer

Salt-doped polymer electrolytes can replace the flammable liquid electrolytes enhancing safety and chemical stability. The challenges to apply the polymer electrolytes to commercial batteries are dendrite formation and the low ionic conductivity. Understanding the ionic transport is essential to design high-performance batteries. Limitations of the conventional electrochemical measurements arise as the system gets complicated. Accurate and straightforward way to measure the transport properties is required. We successfully applied the measurement technique using time-resolved Fourier Transform infrared - attenuated total reflectance (FTIR-ATR) spectroscopy to polymer electrolytes. The diffusion coefficients of lithium salt through a polystyrene-poly(ethylene oxide) block copolymer (SEO) electrolytes were investigated. Since the concentration gradient is the only driving force, the diffusion coefficient could be decoupled with the ionic conductivity and transference number. The results showed non-monotonic dependence of the diffusion coefficient on the salt concentration implying the polymer structure or ion dissociation plays a role in the diffusion in concentrated polymer electrolyte.